This invention relates to liquid crystal materials having a wide liquid crystal temperature range and a positive dielectric anisotropy, and to a liquid crystal composition containing them.
Liquid crystal display elements utilize optical anisotropy and dielectric anisotropy, which are characteristics of the liquid crystal material. There are many types of liquid crystal display elements, such as TN (twist nematic) type, DS (dynamic scattering) type, guest-host type and DAP type, etc., in which required characteristics of the liquid crystal materials are different according to their types. In any type, however, it is necessary that the liquid crystal materials are stable to moisture, heat, air and light, etc. and also it is desirable that they show liquid a crystal phase in as wide a temperature range as possible. To date, there has not been found any single compound which can satisfy these conditions, and it is the present status of this art that the compounds obtained by mixing several kinds of the liquid crystal materials are utilized. Recently, a display device operable from low temperature (about -20.degree. C.) to high temperature (80.degree..about.90.degree. C.) is particularly required, but it is difficult to satisfy such a requirement by any combination of known compounds.
The compounds of this invention were intended to satisfy such a requirement.